1. Field of the Invention
This invention relates to a container and, more particularly, to a divided food container used for packaging food during refrigeration which may also be used during the subsequent heating and serving of the packaged food.
2. Description of the Prior Art
There is a demand for a container wherein meals consisting of different foods are packaged and refrigerated for a substantial length of time and subsequently prepared and served within a minimum length of time. Such a container is particularly needed for meals which are to be served on airliners and at institutions such as schools and hospitals, as well as homes wherein food may be reheated in a microwave oven. Separate, premeasured portions of food must be stored in the container under refrigerated conditions for extended periods of time and then quickly reheated and served.
Such a food container must be low in cost, disposable, and adapted to protect the packaged food stored therein under conditions of the extreme temperature variations.
Heretofore, the majority of prior art food containers used for such purposes were made completely from plastic or metal foil. Although metal foil and plastic can be used to form food packaging containers their use has certain disadvantages. For example, the preferred method at present for reheating premeasured food portions disposed in such containers is through the use of microwave ovens. One advantage of microwave ovens is that the food within the container can be heated without necessarily heating the container in which the food is packaged. Thus, the use of metal foil as the packaging material nullifies this advantage in that a microwave oven will heat both the food and the metal food container, making the container difficult to handle. Additionally, the use of metal food containers tends to short circuit microwave radiation, reducing the effectiveness of the oven.
With regard to food containers constructed solely from plastic materials, the material and manufacturing costs for producing a sufficiently rigid container are higher than the material and manufacturing costs associated with the use of paperboard as a container material. The packaging operation by which the food products are sealed in individual containers should be highly automated and should employ low cost materials to reduce packaging costs without reducing the integrity of the package seal. Paperboard is strong and relatively inexpensive and therefore generally suitable for such packaging applications.
It has been found that if a paperboard food container is lined with a continuous sheet of film, such as polypropylene or polyethylene, the film would tend to rigidify the container and further tends to lock flanges formed on such a container in place, which can be associated with a lid for the container. The film has been formed in place after the container has been erected from a paperboard blank which lends the formation of such containers to low cost, mass produced, manufacturing operations.
U.S. Pat. No. 3,932,105, issued Jan. 13, 1976, and assigned to the assignee of the present invention, discloses equipment and a process for lining an erected paperboard food container with a continuous sheet of film. In a preferred embodiment, the film is heated and then drawn into intimate contact with the interior tray walls by applying a vacuum to the exterior bottom wall and exterior side walls of the tray.
U.S. Pat. No. 3,863,832, issued Feb. 4, 1975, illustrates a paperboard food container of the type discussed above, which might be useful in such a manufacturing process. The food packaging container disclosed therein includes a tray and a lid both of which are constructed of paperboard having a thermoplastic coating on at least the interior surface thereof. The tray includes a base portion and a plurality of upstanding walls. The base portion is rectangular with four divergently upstanding walls which are foldably connected to the base portion. The upstanding walls are traversely interconnected by corner closures. Each corner closure is foldably connected to an upstanding wall at one end thereof and is overlappingly bonded to the transverse end of the adjacent upstanding wall. Each of the upstanding walls is foldably connected to a horizontal panel. The ends of the horizontal panels are abutting so as to form a horizontal, peripheral flange. A lid may then be bonded to the peripheral flange to seal food contents placed within the container. In one embodiment, an upstanding central divider wall is provided in the rectangular base portion to provide a pair of discrete compartments for holding different food portions.